1. Field of the Invention
The present invention relates to an apparatus and a method of controlling clock frequency generation, and more particularly, to an apparatus and a method for a portable device.
2. Background of the Related Art
In general, a portable device such as a notebook computer can be supplied with its necessary electric energy either by a battery or an AC power line. However, because battery capacity is limited, a notebook cannot be used for more than a few hours if its power is supplied from the battery.
FIG. 1 is a simplified block diagram of a related art notebook. The notebook of FIG. 1 comprises a CPU 11 conducting ordinary well-known operations and functions; a bridge controller 12 conducting both assistant operations of the CPU 11 and management of memories, a video port, a bus, etc.; a video processor 13 for processing video data and outputting the processed data for video presentation; and a clock generator 10 providing a 100 MHz clock signal 1 for the CPU 11 and the bridge controller 12, and a 66 MHz clock signal 2 for the video processor 13.
A PLL (Phase Lock Loop) circuit 110 is embedded in the CPU 11. The PLL circuit 110 multiplies the 100 MHz clock from the clock generator 10 differently based on a current power supplying mode. For example, the PLL circuit 110 multiplies the 100 MHz clock 1 by a factor of six to produce a 600 MHz internal clock if an AC power mode (PWR mode) is detected, and it multiplies the 100 MHz clock 1 by a factor of five to produce a 500 MHz clock if a battery power mode is detected.
Because power consumption of a CPU 11 is proportional to the speed of a clock driving the CPU 11, if a 500 MHz internal clock is used in a battery supplying mode, processing speed is lowered and power dissipation is decreased in comparison with a 600 MHz internal clock. Therefore, battery life is extended.
However, in a related portable computer, a host bus 3 to which both a CPU 11 and a bridge controller 12 are connected is driven by a bus clock to bridge controller 12 whose speed is fixed regardless of power supplying mode. Therefore, power saving in a battery supplying mode is less effective.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.